How to Read and File a Vehicle Diagnostic Report

A vehicle diagnostic report is a dated record of what a scan tool and technician found when they checked a car's onboard systems. To read one, first confirm that it belongs to your vehicle. Check the vehicle details, the date and the mileage. Next, look at the exact fault codes and their descriptions, any live data, and any notes or inspection history. To file it, keep the original document unchanged, record those key fields in a simple log, and store the report with its attachments in your service records. A fault code on the report is not a confirmed diagnosis. It shows what the vehicle's systems flagged. A technician still has to interpret it, and what it means can depend on the make, model, model year and equipment.

What a Diagnostic Report Is, and What It Is Not

Most reports are built around diagnostic trouble codes (DTCs). A DTC is a short alphanumeric code that a vehicle's control modules store when they detect a condition outside their expected range. A technician reads these codes with a scan tool and interprets them with diagnostic software, which can add details about the reported issue. The report records that process at a single point in time.

The report does not tell you on its own why a code was set or what repair is needed, if any. Treat the report as evidence to keep accurately. This guide covers reading the report as a document and filing it. It does not cover the technical meaning of individual codes. Verify code definitions against the manufacturer's service information for your specific vehicle, or ask the technician who produced the report.

Check the Scope of the Diagnostic Before Reading the Results

Diagnostics vary in scope and depth. A minor or basic diagnostic is typically a quick scan with a diagnostic tool to check for stored codes. A more in-depth diagnostic may add live data review, further testing and technician notes. Before you draw any conclusion from the results, find out which kind of check the report records. A report with no codes from a quick scan is not the same as a full inspection that found no faults. If the report doesn't state its scope, note that as a gap and ask the shop.

Fields to Identify on the Report

Reports differ by shop, tool and manufacturer, so the layout and labels on yours may not match this list. A complete report generally includes the items below. If one is missing, record it as missing rather than filling it in from memory.

Field | What to record | Why it matters

Vehicle details | Make, model, model year, VIN if shown, and any model type code exactly as printed | Confirms the report belongs to your vehicle; code meanings can vary by vehicle

Date | Date of the scan or inspection | Places the findings on a timeline with other service records

Mileage | Odometer reading with its unit (miles or kilometers) | Ties findings to vehicle use; the unit matters if the report came from a tool or shop that uses a different unit

Tools and software | Scan tool or software named on the report, if listed | Different tools can present codes and descriptions differently

Scope | Type of check performed, such as a quick scan or a more detailed diagnostic | Shows how much the results can support

Diagnostic trouble codes | Every code exactly as printed, character for character | Small transcription errors can change what a code refers to

Code descriptions | The description text as printed next to each code | Preserves the tool's interpretation at the time of the scan

Code status or module | Any status label or system/module name shown with a code, copied as written | Context that a technician may need later; verify what each label means for your tool

Live data | Values such as engine RPM, with units and the conditions noted | Snapshot readings only make sense with their units and context

Inspection history and notes | Prior results listed on the report and any technician comments | Shows whether findings repeat across visits

Shop or technician | Name of the business or person who produced the report | Lets you follow up with questions

How to Read the Code Section Without Over-Reading It

• Copy codes exactly, including letters, numbers and any suffixes. Do not shorten or retype them from memory.
• Keep the printed description with each code. Do not substitute a description from a different source, because definitions can differ by manufacturer and model year.
• Note how many codes appear and whether the report groups them by system or module.
• If the report lists more than one set of results, such as numbered diagnostic results or multiple inspection dates, keep each set separate and note its date.
• If a code or label is unfamiliar, mark it for follow-up. Do not guess at its meaning; check it against verified terminology and service information for your exact vehicle.
• Do not treat a code as proof that a particular part has failed. A code records a detected condition. A technician has to identify the cause.

Reading Live Data Entries

Some reports include live or recorded data, which are sensor and system readings captured during the scan, such as engine RPM. Record each value with its unit and any condition the report lists, such as idle or a specific temperature. A single reading has no meaning without the specification for that vehicle and the operating conditions when it was taken. Keep the values as evidence and leave interpretation to someone with the correct specifications.

How to File the Report

• Keep the original file or paper copy unchanged. If you receive a PDF, save it as delivered and avoid editing, annotating or re-exporting the original.
• Put annotations in a separate copy or a separate notes file.
• Name files consistently, so reports sort by date and the vehicle can be identified at a glance.
• Store attachments together with the report. Attachments include printouts, live data exports, photos and the related invoice or work order.
• Add a one-line entry to a service log that summarizes the key fields, so you can scan history without opening every file.
• Keep a backup copy in a second location.
• Keep the report with the vehicle's other service records, so they can go to a future owner or a repair shop as one set.

A naming pattern and log entry like the following keep records consistent. The bracketed items are placeholders, so replace them with the values printed on your report.

File name:
[YYYY-MM-DD]_[make-model-year]_[mileage+unit]_diagnostic-report.pdf

Log entry:
Date:        [YYYY-MM-DD]
Vehicle:     [make / model / model year / VIN or model type code]
Mileage:     [value] [mi or km]
Performed by:[shop or technician]
Tool/scope:  [tool or software, if listed] / [quick scan or detailed diagnostic]
Codes:       [code] - [description as printed]
Live data:   [attached / not included]
Attachments: [list of files]
Open items:  [unfamiliar codes or questions for the shop]

Limits of This Guide and Gaps to Resolve

• Code meanings: This guide does not define individual codes or status labels. Verify them against authoritative terminology and the manufacturer's service information for your model year, market and powertrain.
• Retention periods: No verified guidance on how long to keep diagnostic reports was available for this guide. Check with your warranty provider, insurer or the vehicle manufacturer if you need a specific period.
• Legal or warranty requirements: Any documentation requirements depend on jurisdiction and the terms of your warranty or service contract. Confirm them with the relevant authority or provider.
• Report format: Layouts and field names vary by shop and tool. If your report is missing a field listed here, ask the issuer whether that information exists.

If the report leaves questions about what was checked, what a code refers to, or whether any action is needed, ask the shop or technician who produced it. They have the full context of the scan, and they can explain their findings for your specific vehicle.